Gastrointestinal stromal tumors (GISTs) are generally considered resistant to radiation, but no prospective trials addressing efficacy and tolerability of radiation therapy have been carried out. Limited clinical experience suggests that selected GIST patients may benefit from palliative radiation therapy. The purpose of this prospective, non-randomized, multicenter study is to evaluate efficacy and safety of palliative radiation therapy in GIST patients who have progressive GIST during or after tyrosine kinase inhibitor therapy.

Radiation therapy planning must be based on computerized tomography (CT). External beam radiation must be used. Both 3D and IMRT plans are acceptable. The cumulative radiation dose may range from 30 to 40 Gy as administered in 1.8 to 2.0 Gy fractions, 5 fractions per week. The dose is specified as defined by the ICRU (International Commission on Radiation Units and Measurements) report 50. Response is evaluated using CT 6 and 12 weeks after irradiation. Adverse effects are evaluated using the Common Terminology Criteria for Adverse Effects (CTCAE)version 3.

Inclusion Criteria:

• Histologically verified GIST.
• Metastatic or locally advanced, inoperable disease.
• Adequate systemic treatment has been administered.
• One or more growing GIST metastasis present during of after TKI therapy.
• The target lesion(s) is measurable.
• A written informed consent

Exclusion Criteria:

• WHO performance status is 4.
• Estimated life-expectancy less than 3 months.
• Radiation planning target volume greater than 3 dm3.
• Unmeasurable target lesion. Bone and brain metastases are not accepted target lesions.
• Radiation therapy cannot be delivered (e.g. active infection or restlessness.)
• Pregnancy.
• Systemic GIST treatment with unknown efficacy.
• Copies of CT images cannot be sent for central review.